1. Field of the Invention
The present invention relates to a semiconductor device including a bipolar junction transistor, and a production method for producing such a semiconductor device.
2. Description of the Related Art
As a representative type of bipolar junction transistor (BJT), an emitter-grounded type high frequency BJT is well known. For example, the emitter-grounded type high frequency BJT is disclosed in Japanese Laid-Open Patent Publications (KOKAI) No. SHO-64-073669 and No. HEI-10-247713.
As disclosed in these publications by way of example, the emitter-grounded type high frequency BJT comprises a p+-type substrate, a p−-type epitaxial layer formed on the p+-type substrate, and an n−-type epitaxial layer formed on the p+-type substrate. The p−-type epitaxial layer has a collector-buried region formed therein, and the n−-type epitaxial layer has a collector-contact region formed therein and electrically connected to the collector-buried region. Also, the n−-type epitaxial layer has a base region formed therein and disposed above the collector-buried region, and an emitter region formed in the base region. Further, the p−-type epitaxial layer has a p+-type buried diffusion region formed therein beside the collector-buried region, and the n−-type epitaxial layer has a p+-type channel stopper region formed therein and electrically connected to the p+-type buried diffusion region.
The BJT also comprises an insulation layer formed on the n−-type epitaxial layer. Three openings are perforated in the insulation layer such that the collector-contact, base, and emitter regions are exposed to the outside, and are filled with a suitable conductive material, resulting in formation of collector, base, and emitter electrodes electrically connected to the respective collector-contact, base and emitter regions. Also, an additional opening is perforated in the insulation layer such that the p+-type channel stopper region is exposed to the outside, and is filled with a suitable conductive material, resulting in formation of a sub-emitter electrode electrically connected to the p+-type channel stopper region.
The BJT further comprises a wiring pattern formed on the insulation layer, and the wiring pattern includes a conducting path for connecting the emitter electrode and the sub-emitter electrode to each other. Thus, the emitter region is connected to the p+-type substrate through the intermediary of the emitter electrode, the conducting path, the sub-emitter electrode, the p+-type channel stopper region, and the p+-type buried diffusion region. Namely, the electrical connection of the emitter electrode to the p+-type substrate is established in an interior of the BJT without using any bonding-wire.
Usually, the p+-type substrate has a metallized layer formed on the bottom or rear surface thereof, with the metallized layer being suitably grounded when the BJT is used. Namely, the grounding of the emitter region is carried out without using any bonding-wire.
As is apparent from the foregoing, in the above-mentioned conventional BJT, no bonding-wire is used to establish the electrical connection for the emitter electrode. Thus, it is possible to considerably suppress an increase of impedance and a voltage drop, in comparison with a case where a bonding-wire is used to establish the electrical connection for the emitter electrode. Therefore, in the BJT, a high-frequency characteristic and gain can be considerably improved.
On the other hand, the conventional BJT is provided with a base-bonding pad and collector-bonding pad formed on the insulation layer, the respective base-bonding and collector-bonding pads are connected to the base and collector electrodes by conducting paths included in the aforesaid wiring pattern. After the BJT is mounted on a lead frame, the respective base-bonding and collector-bonding pads are electrically connected to predetermined leads of the lead frame, using bonding-wires. Each of the base-bonding and collector-bonding pads has a considerably larger size in comparison with the size of the base and collector electrodes, such that the bonding wires can be surely bonded to each pad.
With the arrangement of the aforesaid conventional BJT, the base-bonding pad may be placed above the high resistance p−-type epitaxial layer such that the insulation layer and the channel stopper region or high concentration p+-type diffusion region are intervened therebetween. Thus, when thermal noises are generated in the p-type epitaxial layer, they are input to the base-bonding pad through a parasitic capacitance produced due to the insulation layer which serves as a dielectric, resulting in decline in a noise factor (NF) characteristic of the BJT.